`Webrick` `1.8.0` is incompatible with `rack` `2.2.6.2`, because it introduced "frozen" strings. Version `1.7.0` still works. You can find a minimum example [here](https://github.com/ThomasKoppensteiner/rack-webrick-frozen-str-issue). > Response array must now be non-frozen. States `rack` in the [upgrade guide](https://github.com/rack/rack/blob/main/UPGRADE-GUIDE.md#rack-2--rack-3-compatibility).
Webrick1.8.0is incompatible withrack2.2.6.2, because it introduced "frozen" strings.Version
1.7.0still works.You can find a minimum example here.